1. Field of the Invention
The invention relates to an electric motor and a method for finding the position of an armature in relation to a stator of the motor, in the case of which the armature is driven by an exciting field which is produced by exciting windings of the stator, and the armature is caused by the exciting field to perform an oscillatory motion, whose progression is detected by a position measuring means for measuring positions of the armature and is evaluated to determine the relative position.
2. Description of the Related Art
Such a method is for example described in the German patent publication DE 103 15 754 A1. In the known method which is for example applicable to rotary drives, a phase relationship between the current serving for production of the exciting field and mechanical oscillations of the armature, is evaluated. The correlation results in a measure for the relative position of the armature to the stator. Between the oscillations, which are produced by the current, and the oscillation response of the armature however undesired phase differences may occur, as for example owing to the effects of friction, loads coupled with the armature and the like, which influence the oscillation characteristics. Accordingly there are errors in measurement. The position of the armature in relation to stator can not be correctly found.
A knowledge of the position of the armature in relation to stator is however essential for effective operation of the motor. On the basis of a correctly found relative position the respective motor will operate in an optimum fashion. The relative position, which in the case of a linear motor is a linear distance between the armature and the poles of the exciting field, and in the case of a rotary motor is an angle between the poles of the armature and of the exciting field, corresponds to a commutation effect, which is employed for the supply of current to the exciting windings. When for instance a constant but incorrect commutation offset between the armature and the stator is taken as a basis, the power output of the motor will be reduced.